A WCDMA mobile communication system provides a Multimedia Broadcast/Multicast Service (MBMS) to user equipments (UEs). The MBMS is a service for transmitting data packets to users.
FIG. 1 is a block diagram illustrating the configuration of a WCDMA mobile communication system supporting such an MBMS.
The WCDMA mobile communication system includes at least one UE 10 and/or 12 for receiving the MBMS, a UMTS Terrestrial Radio Access Network (UTRAN) containing a node B 20 and a radio network controller (RNC) 30, a Serving GPRS Support Node (SGSN) 40 belonging to a core network (CN), a Home Location Register (HLR) 42, a Gateway GPRS Support Node (GGSN) (not shown), and a packet network 50 for transmitting packet data.
The UE 10 or 12 is connected to the node B 20 and the UTRAN so as to process a call, supports both circuit service (CS) and packet service (PS), and includes hardware and software for receiving MBMS data. The node B 20 is connected to the UE 10 or 12 via a Uu interface, and the RNC 30 is connected to the SGSN 40 via an Tu interface.
The UTRAN performs a protocol conversion process to transfer radio frequency (RF) data control messages, transmitted from the UE 10 or 12 over the air, to the CN using a GPRS Tunneling Protocol (GTP). In this case, the GPRS (General Packet Radio Service) is a packet data service provided in the UMTS network. The SGSN 40 is a network node for managing subscriber and position information of the UE 10 or 12. The SGSN 40 is connected to the UTRAN via an Iu interface, and transmits/receives data, control messages, etc. to/from the packet network 50. The SGSN 40 is connected to the HLR 42 via a Gr interface, and manages the subscriber information and position information. The HLR 42 stores subscriber information of a packet domain, routing information, etc. The HLR 42 is connected to the SGSN 40 via a Gr interface. A message flow for transmitting/receiving packet data in a WCDMA mobile communication system having the aforementioned construction will now be described with reference to FIG. 2.
First, in order for the UE 10 and the RNC 30 to transmit or receive packet data therebetween, a radio resource control (RRC) connection must be set between the UE 10 and the RNC 30.
The RRC connection set between the UE 10 and the RNC 30 may have one of three states (i.e., a CELL_DCH state, a CELL_FACH state, and an IDLE state) and transitions between the CELL_DCH state, the CELL_FACH state and the IDLE state according to the volume of packet data traffic transmitted and received between the UE 10 and the RNC 30.
The CELL_DCH state refers to a 3GPP WCDMA RRC state, and represents a state in which the RRC connection and a dedicated physical channel are connected between a UE and a node B (i.e. UTRAN) in a WCDMA network. In the CELL_DCH state, a large amount of packet data is actually transmitted or received.
The CELL_FACH state refers to a 3GPP WCDMA RRC state, and represents a state in which the dedicated physical channel is released and the RRC connection is maintained. In the CELL_FACH state, an S-CCPCH (FACH) is continuously monitored, and a small amount of uplink or downlink packet data can be transmitted or received.
The IDLE state represents a state in which both RRC connection and dedicated physical channel have been released. In the IDLE state, only a paging indication channel (PICH) is monitored, and it is possible to enter a WCDMA protocol sleep state.
Referring to FIG. 2, the UE 10 transmits an RRC connection setup request message to the RNC 30 in step 102. When receiving the RRC Connection Setup Request message, the RNC 30 transmits an RRC Connection Setup message to the UE 10 in step 104. When receiving the RRC Connection Setup message, the UE 10 transmits an RRC Connection Setup Complete message to the RNC 30 in response to the RRC Connection Setup message, thereby setting an RRC connection between the UE 10 and RNC 30.
Then, the UE 10 performs a packet data protocol (PDP) Context Activation procedure for packet data communication. In detail, the UE 10 transmits a PDP Context Activation Request message to the SGSN 40 in step 108. When receiving the PDP Context Activation Request message from the UE 10, the SGSN 40 transmits a PDP Context Activation Accept message to the UE 10 in step 110, thereby enabling the UE 10 to perform packet communication.
After the PDP Context Activation procedure, uplink and downlink packet data traffic is transmitted between the UE 10 and the SGSN 40 in step 112. Thereafter, when there is no packet data traffic transmitted between the UE 10 and the SGSN 40 in step 114, the RNC 30 changes a state of a physical channel established between the UE 10 and RNC 30 in step 116. In other words, when the volume of packet data traffic transmitted to or received from the UE 10 is reduced, the RNC 30 transitions to the CELL_FACH state. Subsequently, when the RNC 30 determines that there is no more packet data traffic transmitted in step 118, the RNC 30 proceeds to step 120, where the RNC 30 transmits an RRC Connection Release message to the UE 10. In response to the RRC Connection Release message, the UE 10 transmits an RRC Connection Release Complete message to the RNC 30 in step 122, so that the RRC connection transitions to the IDLE state.
As described above, according to the conventional WCDMA 3GPP standard, while packet data is being transmitted/received after signaling for transmission of packet data has been achieved between the UE 10 and the SGSN 40, if the volume of packet data traffic is reduced, the RNC 30 releases the RRC connection, and instructs the UE 10 to transition the RRC state from the CELL_FACH (or CELL_DCH) state to the IDLE state.
Through this, the UE 10 releases the RRC connection, and transitions from the CELL_FACH (or CELL_DCH) state to the IDLE state, thereby entering a sleep state in terms of protocol. When the UE 10 has entered the sleep state, power consumption is minimized, so that it is possible to stably manage the battery thereof.
However, some WCDMA networks have a problem in that they do not release the RRC connection or that they release the RRC connection too late, although there is no more packet data traffic being transmitted in the CELL_FACH state.
According to the conventional technology, there is no way for the UE 10 to transition from the CELL_FACH state to the IDLE state, except for following the control of the network. Therefore, the UE 10 must continuously monitor a dedicated control channel (DCCH), a radio access channel (RACH) and a forward access channel (FACH) while in the CELL_DCH state, and must continuously monitor the FACH and the RACH while in the CELL_FACH state, so that unnecessary current consumption is caused, thereby decreasing the battery lifetime.
Also, among smart phones recently highlighted in the 3G market, WinCE-based phones have a menu which is configured in such a manner as to release a cellular connection by a wireless manager, so that the WinCE-based phone does not release the PDP connection, even when the End key is pressed, unlike other general phones, thereby having a high probability of causing the aforementioned problem.